1. Field of the Invention
The present invention relates to a method and a circuit for searching for a pitch period of a speech signal to determine coefficients for a long term predictor which is used in a coder and decoder (codec) for speech signals.
2. Description of the Related Art
Recently, high performance speech coding, wherein speech signals can be transmitted at low bit rates without remarkably degrading quality of the speech signals, have been required in local communication systems, digital mobile communication systems, and the like.
In several types of speech coding, for example, code-excited linear predictive coding (CELP), residual-excited linear predictive coding (RELP), and multi-pulse excited linear predictive coding (MPC), a long term predictor (pitch predictor) is used for performing long term prediction based on periodicity of a speech signal.
Coefficients for the long term predictor are determined by minimizing a total squared prediction error after pitch prediction. Accordingly, the total squared prediction error for all pitch periods which are probable in speech signals had to be estimated to find the most adequate coefficients for each speech signal block. Therefore, the number of arithmetic operations becomes enormous and the scale of required hardware becomes large.